It is known that the polyurethane systems used for producing moulded articles exhibit strong adhesion to the employed mould materials, typically highly thermally conductive materials such as metals. Demoulding of the moulded polyurethane articles therefore requires release agents which are applied to the mould walls which come into contact with polyurethanes and/or the polyurethane reaction mixture.
Such release agents may be for example dispersions or emulsions of waxes, soaps, oils and/or silicones in solvents such as hydrocarbons or water.
After application of the release agent to the mould the solvent evaporates and the non-volatile release-active substances form a thin release film intended to ensure that the moulded polyurethane article may be easily removed from the mould after production.
In addition to the actually required release action the release agent also assumes further functions and thus also very strongly influences the surface of the moulded polyurethane article which is intended to be fine-pored/smooth and uniform in order inter alia to ensure good coverability of the finished moulded articles with textiles or leather.
In order to reduce environmental pollution with organic material there is a great interest in aqueous-based release agents free from volatile organic material. However, compared to conventional release agents comprising organic solvents the aqueous release agents on the market often have the disadvantage that after evaporation of a large part of the water a thin water film which is not volatilized at the typical mould temperatures of 45° C. to 80° C., preferably 50° C. to 75° C., is always left behind in the mould and undergoes reactions with isocyanate compounds of the polyurethane system which result in very hard polyurea compounds. This can result in disruption of the mould surfaces due to so-called buildup which needs to be removed by costly and inconvenient cleaning.
Typical examples of aqueous release agents having a good demoulding action are described for example in DE A 37 42 370 or DE A 40 20 036. These agents comprise as the release-active substance unsaturated oligomeric or polymeric hydrocarbons having molecular weights of at least 500 and iodine numbers of at least 60, particularly preferably liquid polybutadiene having molecular weights of about 3000 and iodine numbers of about 450. EP 1785251 describes the use of polyisobutylenes in release agents.
These release agents have an oily character which has the result that the surface of the moulded polyurethane article feels oily. This is not just a haptic deficiency but also a technical one since the surfaces also have only poor adherability so that for example sensors may be bonded to the relevant surfaces of moulded polyurethane articles only with difficulty, if at all.